How-To: USD Fork Assembly

[TSM]

This is a general How-To on assembling a USD fork. Specifically this is a fork from a ZX7R P1, but the basics can be applied to most USD forks, refer to the service manual regarding the specifics of your forks.

WARNING: This is a safety critical service item, if you are unsure or worried about doing anything shown below, STOP. Take your bike to a professional or seek help and advice from someone qualified. I take no responsibility for anyone following these instructions, take the following as an outline basic guide.


Tools/Parts
Socket set & Wrench
Spanners or Adjustable Spanners
Allen keys
Impact drill
Torque wrench (5-50Nm)
Drain pipe
Locktight
Plastic freezer bag
Some Wire
Fork oil
Seals

All parts of fork, disassembled.
From top, Fork Inner Tube/Lower Leg, Outer Fork Leg, Rebound Damper Rod, Fork Cartridge, Pre-load Cap/Rebound Adjuster, Oil Seal, Cartridge Retaining Bolt+Copper Washer, Outer Fork Bush, Inner Fork Bush, Oil Seal Retaining Clip, Spring Retaining Washer, Spring, Steel Bush Retaining Ring, Dust Seal. The grey tube will be used later.


The fork has already been disassembled, its roughly the reverse of assembly, the oil has to be dumped, the fork cartridge retaining bolt has to be removed, if you have a impact drill it will assist in this, to pull the two half's of the fork apart after the cartridge has been removed, take the fork oil seal retaining clip off and pull the two half's apart, you may have to slide the tubes apart a few times till the bushes come out. To take the inner fork bush off you can use a flat headed screwdriver to pry the split apart, take care not to damage the bush. If you are not going to reuse the oil & dust seal, just pull them off, if you plan to reuse the oil or dust seal you will need to use the plastic bag to safely take the seal off the tube without damaging it. Thats how to disassemble the fork.


Step1
Take Fork Inner Tube, place a small plastic bag over top of tube, coat the bag with some fork oil.
This is to make sure that when you put the new oil & dust seals on the fork, the sharp edges of the tube do not damage the seals.


Step2
Take your dust & oil seals, apply some oil to the inner parts, slide over end of fork. Take care as the seals damage easily.
Dust seal goes first, oil seal after.


Step3
Take plastic bag off. Put fork bush retaining ring next, then outer bush.
The inner bush is split, you carefully pull it over the top of the tube and set it in the grove where it will fit firm.


Step4
Slide outer fork tube over inner tube.


Step5
Peice of drain pipe that has been cut to size,rough edges smoothed down and a cut along the length of the tube to allow it to be fitted onto the fork. This is your makeshift "fork bush driver"
Turn fork upside down.
Place the fork bush driver on the inner fork tube with the fork bush retaining ring below the driver. Holding the fork straight, tap downwards on the makeshift fork bush retaining ring until the bush is firmly in place.


Step6
I am using my old fork oil seal here to put the new oil seal in, usually you will pull the forks apart to change both oil and dust seals, but in the case that you are only doing the dust seals and reusing the oil seals, use the v fork bush driver tool to carefully put in the oil seal.
Ive cut the old seal so i can take it off the fork when I am done.


Step7
Fit fork oil seal retaining clip


Step8
Push the fork dust seal into place, usually this can be pushed with your fingers, if not you can use the makeshift fork bush driver tool.


Step9
Put fork cartridge into fork


Step10
If you dont have the correct tool to stop the cartridge from rotating then putting the spring in the fork will assist with the next step.


Step11
Use some blue locktight on the fork cartridge retaining bolt. I happen to reuse my copper washer but the service manual says that its a item that should be replaced. Make sure there is no debris on the washer or it will not seal correctly.


Step12
Using a long allen key fitted to a socket (i cut a old allen key i had), torque up the cartridge retaining bolt, if you are not getting any resistance, push the fork down so there is resistance on the cartridge by the spring you put in.


Step13
Fill fork with oil. Look in the service manual for the type of forks you have for all the specifications on what oil and how much oil you require.


Step14
Pull the damper rod up and down many times to fill the cartridge up with oil and remove air, leave fork standing for a few mins for all air bubbles to rise to the top. You will feal a constant resistance and no bubbling when all the air is gone and oil in the cartridge.


Setp15
Most forks are not filled with oil to the top when fully compressed. In the case of these forks, the oil level is measured from the top of the outer tube when its fully compressed and without a spring or rebound adjuster rod installed.


Step16
We need to hold the damper rod up so that once we place the spring into the fork we can fit the fork cap. Here I am using some wire, wrapped around the tube.


Step17
Slowly put spring over wire and into the fork, note that some forks require the spring to be placed a certain way around. Do not drop the spring as oil will splash out and you will have to check the level again.


Step18
Not all forks need this bit. The spring needs to be compressed so we can fit the fork adjuster cap. Im using a adjustable spanner here set to narrower than the nut.


Step19
Most fully adjustable forks have a requirement spec that the nut is a certian spacing from the top, this is so both forks have the same adjustment at a given setting.


Step20
The spring retaining washer has been placed along with the fork adjuster cap which has been wound down by hand.


Step21
Using two spanners, one to hold the nut on the damper rod, one on the adjuster. You need to tighten the two together, usually forks will specify that the damper rod nut is held in place and the adjuster is turned till its tight. Here is about 10-15Nm, you will just have to judge that for your self if your fork adjusters have only two flats on the top, some have the ability to put a socket on, in that case use the spec torque figure.


Step22 (The Lunge)
Da daaaa, all put together.


Step23
Screw the fork adjuster cap onto the outer fork tube and torque up to spec. If you cant do this easily then put fork back on bike, pinch up the bottom yoke bolt leaving top ones loose and tighten.



All Done
Thats it, all done. This is only a general guide, read warning at top before you consider attempting this yourself.

[yorkie_chris]

SRAD6 forks require the rebound adjuster to be set at 1 and a bit mm showing above the top with the punch marks aligned. Then you screw the adjuster/cap assembly onto the damper rod until it bottoms, then nip up the locknut. This gives the correct range of adjustment.
I believe the same applies to the USDs on the SRAD750

I think this step is main difference between any type/make of forks.

Cool show there!! I know my showa forks require some damn annoying tools though to hold the spring out of the way while working on them though. ha ha

Nice write up, and I see you got the one of me lunging! lol

Good write up!

I just did exactly that on a ZX7R P1 - spooky. Previous owner had neglected to set the rebound damper adjuster correctly before re-assembly (step 19).

Nice and handy... something for the knowledge base me thinks.